The technology disclosed herein generally relates to fiber optical networks that enable communication between electrical components.
An optical fiber is a cylindrical dielectric waveguide that transmits light along its axis. The fiber consists of a transparent core surrounded by a transparent cladding layer (hereinafter “cladding”), both of which are made of dielectric materials. Light is kept in the core by the phenomenon of total internal reflection. To confine the optical signal in the core, the refractive index of the core is greater than that of the cladding. The boundary between the core and cladding may either be abrupt, as in step-index fiber, or gradual, as in graded-index fiber. Optical fibers can be made of glass or plastic.
Optical networking using plastic optical fiber (POF) has advantages over copper wiring in weight, size, bandwidth, power, and electromagnetic immunity. POF has advantages over glass optical fiber (GOF) in ease of handling, installation and maintenance. POF core material can range from acrylate to perfluorinated polymer. POF index profile can range from step index to graded index. POF geometry can range from single core to multi-core. POF core can accommodate single mode (a single optical path in a very small fiber core) to multi-mode (multiple optical paths in a larger fiber core). Using POF may result in appreciable weight savings. The weight savings may be significant for networks onboard vehicles, such as airplanes, where the weight savings may result in reduced fuel consumption and lower emissions.
It is common practice to connect a number of line replaceable units (LRUs) to each other to achieve communication within an avionics system. For example, a number of LRUs in the forward section of a vehicle (e.g., an airplane) have been connected to a number of LRUs in the aft section of the vehicle. Connecting each LRU to every other LRU could result in an unreasonably large number of connections. Additionally, many of the connections between LRUs may be long, resulting in optical losses.
Fiber optic networks have the advantages of higher speed, lower weight and electromagnetic interference immunity over copper networks. Many models of commercial airplanes have fiber optic networks for size, weight and power reduction. In some cases the large number of glass optical fiber (GOF) cables in the airplane is an important factor contributing to high manufacturing cost. To reduce the cost for installing fiber optic network in airplane, there is a need to reduce the number of fiber optic cables used in the airplanes.
A typical solution to reduce fiber count is to use a wavelength division multiplexing (WDM) system. However, typical WDM systems are not compatible with multimode optical fiber currently used onboard commercial transport aircraft. Typical WDM components are designed for use with single-mode fiber. Single-mode fiber has a diameter smaller than 10 microns and therefore is very sensitive to dust, contamination, and misalignment from airplane vibration and shock. WDM components such as multiplexing and demultiplexing array waveguide gratings (AWG) are expensive and not proven for use in harsh avionic environments.